Simona Gallerani

(Osservatorio Astronomico di Roma)

What can we learn from quasar spectra

on the high-redshift Universe?

In collaboration with: T.Choudhury, P. Dayal, X. Fan, A. Ferrara, A. Maselli, R. Maiolino, R.

Salvaterra

21th July 2009 Roman Young Researchers Meeting

The early Universe

TodayBig Bang

Recombinationprocess

The Universe is composed by a very hot and dense mix of particles and radiation

The expansion allows the radiation to decouple from matter and the first atoms to form

CosmicMicrowave

Background

THE COSMOLOGICAL PRINCIPLE

The Universe is homogeneous and isotropic

on large scales

~50 kyr

Cosmic Web

First stars and galaxies originated predominantly in the regions

of intersection of these filaments.They are immersed in the

Intergalactic medium (IGM)

The first stars

HI

HIIHII

HI

Pre-overlap stage

HII

Overlap stage Post-overlap stage

HII

HII

HIHI

HII

Cosmic reionization

R

O

E

What is the epoch of reionization (EOR)?

~100 Myr ≤1 Gyr ~14 Gyr

Quasars: a class of very bright Active Galactic Nuclei

Black Hole

Accretion disk

Dust torus

SunQSO LL 1310

SunBH MM 96 1010

Particularly luminous

in the rest frame near ultra-violet,

i.e. close to the Lyα emission line

The quasar spectra we observe are strongly affected by the intervening material along the lines of sight

The Lyα forest in quasar absorption spectra

Keck telescope

e

obsz

1

REDSHIFT

α=1216 Å )1( ** z

Becker et al. (2003)

QSOs constraints on cosmic reionization

SDSS

~20 QSOs

@ 5.7<z<6.4

6reiz

Fan et al. (2005)

Simulating the Ly forest

Coles & Jones (1991)

Log-Normal model

Reionization model Choudhury & Ferrara (2006)

Optical depth

Density field(ΛCDM)

Neutral hydrogen(TIGM; UVB)

(Voigt profile)

Reionization models

Early Reionization (ERM) Late Reionization (LRM)

7reionz 6reionz

HII

Models testingERM

LRM

Fan et al. (2006)

Songaila (2004) Fan et al. (2002)

Optical depth evolution Transmitted flux

Simulated spectra3.67.5 z

GAPSGAPS

Largest gap width distributionObservations vs Simulations

Low Redshift (zem<6)

ERM LRM

SG, F

erra

ra, F

an, C

houd

hury

(20

07)

High Redshift (zem>6)

LRM

ERM

6.5z3.5z

The Universe is highly ionized at z~6

Quasars: a class of very bright Active Galactic Nuclei

Black Hole

Accretion disk

Dust torus

SunQSO LL 1310

SunBH MM 96 1010

Particularly luminous

in the rest frame near ultra-violet,

i.e. close to the Lyα emission line

The quasar spectra we observe are strongly affected by the intervening material along the lines of sightAND BY THE DUST SURROUNDING THE AGN!

Dust extinction on quasar spectra

Intrinsic spectrum

Dust absorbed spectrum

Dust absorbs preferentially bluer photons, thus reddening the spectra

An example of extincted spectra at z~6

An empirical extinction law for the high redshift dust

Conclusions

Quasar absorption spectra provide a huge amount of information both concerning the ionization level of the intergalactic medium

and the amount of dust present in the host galaxy.

The analysis of ~ 20 quasars at z~6 shows that observations are consistent with a highly ionized intergalactic medium at z~6.

The analysis of ~ 30 quasars at 4<z<6 shows that the properties of dust at these epochs differ from the local Universe.